Promotion of protoporphyrin IX (PpIX) fluorescence by MEK inhibition in animal models of cancer

Yoshioka, Ema (2016) Promotion of protoporphyrin IX (PpIX) fluorescence by MEK inhibition in animal models of cancer. Masters thesis, Memorial University of Newfoundland.

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Abstract

Background: Protoporphyrin IX (PpIX) is an endogenous fluorescence that is accumulated in cancer cells treated with the heme precursor 5-aminolevulinic acid (5-ALA). The cancer-specific fluorescence of PpIX is used to distinguish tumor from normal tissue, which has proven clinically useful during fluorescence-image guided surgery. This study sought to investigate whether modulation of oncogenic Ras/MEK pathway mediates PpIX accumulation in vitro and in vivo. Methods: For in vitro studies, human breast, lung and prostate cancer cells were treated with or without the MEK inhibitor (U0126) for 20 hours, followed with 5- ALA for 5 hours. The cells were lysed, and the PpIX fluorescence accumulated in the cells was measured with a microplate fluorescence reader (λex 405 nm; λem635 nm). For in vivo studies, the 4T1 mouse breast cancer cells were injected into the right hind flank of 8 week-old Balb/c female mice. U0126 (50 μM/Kg) was injected intratumourally to 4T1 breast tumors for 5/8 h followed by 5- ALA injection. Mice bearing 4T1 breast tumors were also injected intraperitoneally with U0126 for 5 or 8. Furthermore, similar experiments were conducted using a HRAS transgenic mice, which develop spontaneous mammary tumors within 3 months old. Results: In vitro, MEK inhibition increases PpIX fluorescence in human cancer cell lines, but not in normal cell lines. The promotion of PpIX fluorescence by MEK inhibition was most commonly observed among human breast cancer cells. In vivo, PpIX accumulation was observed significantly more in the tumors from mice treated with U0126 and 5-ALA (2-3 fold) than those from mice with vehicle control (DMSO/saline) and 5-ALA. Conclusions: In vitro and in vivo treatment of the MEK inhibitor significantly increases the accumulation of PpIX fluorescence in cancer cells which may contribute to improved efficacy of FGS in clinical settings.

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